Diagnostic function for an internal combustion engine

ABSTRACT

A diagnostic function for an internal-combustion engine whose power is set by way of a power-determining signal that is determined from a first signal from a determination device, and a second signal determined by a torque controller, based on engine torque. A selection device sets either the determination device or the torque controller to be dominant for the power determining signal. When the values of the engine torque are not plausible, an error mode is set. With the setting of the error mode, the dominance is retained when the determination device is dominant. When the torque controller is dominant, a change of the dominance takes place.

[0001] The invention relates to a diagnostic function for an internal-combustion engine whose power is adjusted by way of a power-determining signal. For this purpose, a first signal is determined from a desired-value definition by means of a determination device. A second signal is determined from an engine torque by means of a torque controller. By means of a selection device, the determination device or the torque controller will then be set to be dominant for the power determining signal.

[0002] From the applicant's German Patent Application 19953767.4, which is no prior publication, a control circuit structure of the above-mentioned construction is known. Here, the determination device, for example, corresponds to the rotational speed controller. By means of the rotational speed controller, the first signal, for example, a first injection quantity, is determined from the desired rotational speed value definition. A torque controller determines a second signal, for example, a second injection quantity, from the engine torque and a maximally permissible torque. By way of the selection device, that controller is set to be dominant whose calculated injection quantity is the lowest. By means of this control circuit structure, the internal-combustion engine is effectively protected from being overloaded. However, an error in the torque detection or calculation is not yet taken into account in the case of this control circuit structure.

[0003] It is therefore an object of the invention to supplement the control system by a failure prevention device.

[0004] This object is achieved in that an error mode is set when values of the engine torque are not plausible. With the setting of the error mode, the dominance is maintained when the determination device is dominant. While the torque controller is dominant, a change of dominance will then be carried out. According to claim 2, the change of dominance takes place after a transition function. As a further development of the above, it is provided that the engine torque is led from the last plausible value to zero or, as an alternative, the second signal is led from the last value to a high value. The solution according to the invention and its further developments offer the advantage that a failure in the torque detection will not result in an uncontrolled behavior of the internal-combustion engine. In other words, also when the torque detection fails, will a reduced normal operation of the internal-combustion engine be ensured in that the computing of the power-determining signal is continued. By way of the introduction of the transition function, a jump-type form of the power-determining signal is prevented during a change in the dominance. A power-determining signal in the sense of the invention is an injection quantity or a control path of a control rod.

[0005] Another protective measure of the internal-combustion engine in the event of a failure of the torque detection consists of adapting by means of the diagnostic function a limit value curve of the maximally permissible first signal. This limit value curve is adapted to the lower values of the first signal. The internal-combustion engine is thereby operated at a safe power level in that, for example, the injection quantity is reduced.

[0006] A corresponding return function within the diagnostic function reacts to sporadically occurring errors in the torque detection. As soon as plausible torque values are present again and a time period has elapsed, the return will take place to the normal function.

[0007] The figures illustrate a preferred embodiment.

[0008]FIG. 1 is a system diagram;

[0009]FIGS. 2A, 2B are views of the control circuit structure with a rotational speed and torque controller;

[0010]FIGS. 3A, 3B are views of the control circuit with the control system;

[0011]FIG. 4 is a block diagram of the rotational speed controller;

[0012]FIG. 5 is a time diagram;

[0013]FIG. 6 is a program flow chart.

[0014]FIG. 1 is a system diagram of an internal-combustion engine with an accumulator-type injection system (common rail). The diagram shows an internal-combustion engine 1 with a turbocharger and a charge air cooler 2, an electronic engine control unit 11, a first pump 4, a second pump 6, a high-pressure accumulator (rail) 7, injectors 8 connected thereto, and a throttle valve 5. The first pump 4 delivers the fuel from a fuel tank 3 by way of the throttle valve 5 to the second pump 6. The latter, in turn, delivers the fuel at a high pressure into the high-pressure accumulator 7. The pressure level of the high-pressure accumulator 7 is detected by means of a rail pressure sensor 10. Lines with injectors 8 connected thereto for each cylinder of the internal-combustion engine branch off from the high-pressure accumulator 7.

[0015] The electronic engine control unit 11 controls and regulates the condition of the internal-combustion engine 1. This engine control unit 11 has the usual components of a microcomputer system, such as a microprocessor, I/O modules, buffers and memory chips (EEPROM, RAM). In the memory chips, the operating data relevant to the operation of the internal-combustion engine are applied in characteristic diagrams/characteristic curves. The input quantities of the electronic engine control unit 11 illustrated as examples in FIG. 1 are: The maximum combustion pressure plSt (i) which is measured by means of pressure sensors 9; the pressure pCR of the high-pressure accumulator 7, as well as a signal FW illustrating the power request. The other input quantities relevant to the operation of the internal-combustion engine 1 are indicated by the reference symbol E. As the output quantities A of the electronic engine control unit 11, the control signals for the injectors 8, corresponding to the injection start SB, a power-determining signal ve, and the control signal ADV for the throttle valve 5 are shown. By way of the throttle valve 5, the feed to the second pump 6 is adjusted.

[0016]FIG. 2A shows a block diagram of the regulating system of the internal-combustion engine 1 with the coupled control circuit structure. The following are shown: A rotational speed controller 14, a torque controller 15, a selection device 16 and the internal-combustion engine 1 with the injection system. By way of a clutch 13, the internal-combustion engine 1 drives an engine load 12, such as a waterjet drive. The tooth angles Phi1 and Phi2 of the clutch 13 are detected by rotational speed sensors 19. From the tooth angle Phi1, the rotational engine speed nMOT is computed by way of a detection/filtering function block 18. From the two tooth angles Phi 1 and Phi2, the engine torque MK is determined and evaluated in the diagnostic block 17.

[0017] The input quantities of the rotational speed controller 14 are: The engine rotational speed nMOT, a rotational speed difference dnMOT and a signal ve2, in the following, called a second signal.

[0018] The rotational speed difference is computed from the rotational engine speed nMOT and a desired rotational speed value nMOT (SW) characterizing the requested power. The second signal ve2 corresponds to the output signal of the torque controller 15. The output quantity of the rotational speed controller 14 is a first signal ve1, such as an injection quantity. This signal is guided to the selection device 16 and the torque controller 15. The input quantities of the torque controller 16 are: The engine torque MK, a differential torque dMK, the first signal ve1 and a controller mode RM. The differential torque dMK is computed from the deviation of the engine torque MK with respect to a maximally permissible engine torque. The output signal of the torque controller 15 is the second signal ve2. This signal is guided to the selection device 16 and the rotational speed controller 14.

[0019] By way of the selection device 16, it is determined which of the two controllers 14 and 15 is dominant. For this purpose, the selection device 16 contains a minimal value selection. By means of the minimal value selection, the first signal ve1 is set as the power-determining signal ve if the first signal ve1 is smaller than or equal to the second signal ve2. In this event, the controller mode RM is to set a first value. This corresponds to an operation of the internal-combustion engine in the rotational speed mode. The second signal ve2 is set as the power determining signal ve if its smaller than the first signal ve1. In this case, the controller mode RM is set to a second value. This corresponds to an operation of the internal-combustion engine in the torque limiting mode. The output signals of the selection device 16 are the power-determining signal ve and the controller mode RM. The power-determining signal ve is guided to the injection device of the internal-combustion engine 1. In the sense of the invention, a power-determining signal ve is the injection quantity or the control path of a control rod.

[0020] The process takes place as follows: When implausible values of the engine torque MN are detected, the diagnostic block 17 sets an error mode FM to one. Implausible values are present, for example, when the signal Phi1 is absent because of a line breakdown. With the setting of the error mode FM, the diagnostic block 17 leads the engine torque MK from the last plausible value according to a transition function to zero. In this case, the transition function may be implemented as a mathematical function or by way of a filter. This transition function is illustrated in FIG. 5 and is explained in conjunction with the latter. As a result of the now decreasing engine torque MK, the torque controller 15 computes a greater value of the second signal ve2. The diagnostic block 17 therefore has an indirect effect on the second signal ve2.

[0021] Consequently, when the rotational speed controller 14 is dominant, it remains dominant. When the torque controller 15 is dominant, the second signal ve2 will be increased until it reaches the value of the first signal ve1. Then a transition takes place with respect to the dominance from the torque controller to the rotational speed controller.

[0022]FIG. 2B shows an alternative to FIG. 2A. In this alternative, a software switch SW is provided. The software switch SW is controlled by the signal error mode FM. In the normal operation—error mode FM equal to zero—, the software switch SW is in the marked position. In this position, the second signal ve2 corresponds to the output signal of the torque controller 15. By way of a feedback path RK, the second signal ve2 is guided to the diagnostic block 17. The feedback path RK is activated only in the normal operation. The value of the signal ve2D corresponds to the value of the second signal ve2. In the case of implausible values of the engine torque MK, the diagnostic block 17 sets the error mode FM to one. As a result, the position of the software switch SW will change. In this position, the second signal ve2 is determined by way of the signal ve2D of the diagnostic block 17. Since, by way of the feedback path RK, the signal ve2D is caused to follow the second signal ve2, no jump-type change of the course of the second signal ve2 takes place when the position of the software switch SW is changed. With the setting of the error mode, the diagnostic block 17 controls the second signal ve2 according to a transition function to a maximal value MAX.

[0023]FIG. 3A shows an alternative embodiment of the block diagram of FIG. 2A. In contrast to FIG. 2A, in the case of this block diagram, the signal ve1 is computed by way of a function block 20 depending on a power request, here the accelerator pedal FP. The function block 20 contains the conversion of the accelerator pedal position to the first signal ve1. For this purpose, corresponding characteristic curves are provided, including a limit-value curve (DBR curve). The input quantities required for the conversion are indicated by means of reference symbol E, for example, the rotational engine speed nMOT, charge air pressure pLL, etc. The further construction and the functionality correspond to that of FIG. 2A, so that the information indicated there also applies here.

[0024]FIG. 3B shows an alternative embodiment of the block diagram of FIG. 2B. In contrast to FIG. 2B, in the case of this block diagram, the signal ve1 is computed by way of a function block 20 depending on a power request, here the accelerator pedal FP. The function block 20 contains the conversion of the accelerator pedal position to the first signal ve1. For this purpose, corresponding characteristic curves are provided, including a limit-value curve (DBR curve). The input quantities required for the conversion are indicated by means of reference symbol E, for example, the rotational engine speed nMOT, the charge air pressure pLL, etc. The further construction and the functionality correspond to that of FIG. 2B, so that the information indicated there also applies here.

[0025]FIG. 4 shows the rotational speed controller 14. The latter has an integrating fraction and is illustrated as an example as a PID controller. In practice, the rotational speed controller may also be constructed as a PI- or PI(DT1) controller. The input quantities of the rotational speed controller 14 are: The rotational speed difference dnMOT, the rotational engine speed nMOT and the second signal ve2. The illustrated rotational speed controller contains three function blocks for computing the P-, I- and D-fraction, corresponding to the reference numbers 23 to 25. By way of the function block 23, the P-fraction ve1 (P) is determined from an input quantity EP and the rotational speed difference dnMOT. By way of the function block 24, the I-fraction ve1 (I) is computed from the rotational speed difference dnMOT, a first input signal ve(M) and a second input signal EI. Here, the I-fraction ve1 (I) is limited to the first input signal ve (M). By way of the function block 25, the D-fraction ve1 (D) is computed from the rotational speed difference dnMOT and an input quantity ED. The first input signal ve(M) corresponds either to the second signal ve2 or to a signal ve1 (KF) depending on which signal has the lower significance. For this purpose, a first function block minimal value 22 is provided. The signal ve1 (KF), in turn, is determined from the rotational engine speed nMOT and additional input quantities E by way of characteristic diagrams 21. A limit-value curve (DBR curve) is also contained. The additional input quantities are illustrated as the collective reference symbol E. The input quantities E may, for example, be the charge air pressure pLL, the rotational engine speed nMOT, etc. All three fractions, that is, ve1 (P) and ve1 (I)- and ve1 (D), are added by way of a summation 26 to a common signal ve1 (S). By way of the second function block minimal value 27, that signal is selected from this signal ve1 (S) and from signal ve1 (KF) which has the lowest significance. That signal corresponds to the first signal ve1.

[0026] The second signal ve2 computed by the torque controller 1S influences the calculation of the integrating fraction ve1 (I) of the rotational speed regulator 14. In order to avoid a direct feedback of the output of the rotational speed controller 14 to the integrating fraction ve1 (I) of the rotational speed controller 14 by way of the torque controller 15, a filtering of the second signal ve2 may be provided. In the event of implausible values of the engine torque MK, the error mode FM is set. This mode has the effect that, by way of the diagnostic function, the second signal ve2 is increased. As a result of the minimal value 22, the signal ve1 (KF) becomes effective even when the torque controller 15 is dominant. In order to protect the internal-combustion engine from excessive values of the signal ve1 (KF), for example, an excessive fuel quantity, by way of the characteristic diagrams 21, the signal ve1 (KF) is adapted to lower values. This takes place in that a limit-value curve (DBR-curve) of the characteristics diagrams 21 is changed.

[0027]FIG. 5 shows a time diagram. Here, the time is indicated on the abscissa and the engine torque MK and the second signal ve2D are indicated on the ordinate. In this case, the measured engine torque MK is illustrated as a solid line. Engine torques MK(1) and MK (2) respectively emitted by the diagnostic block 17 are illustrated as broken lines. The alternative solution is shown as a dash-dotted line, in which the diagnostic block 17 increases the second signal ve2 by way of the signal ve2D. At the point in time t1, the engine torque MK decreases from the value of point A to zero, for example, because of a sensor failure. Starting at the point in time t1, this engine torque MK will then remain at zero. At a point in time t2, the diagnostic function detects that the engine torque MK is no longer plausible. Subsequently, the diagnostic function controls the value of the engine torque MK according to a transition function to the zero value, point B, at the point in time t3. In a first embodiment, this transition function may be constructed as a linear function MK(1). As an alternative, this transition function may also be constructed corresponding to a filtering function MK (2) with a parabolic course. The reduction of the engine torque MK(1) or MK(2) emitted by the diagnostic block consequently causes an increase of the second signal ve2. The diagnostic block 17 therefore acts indirectly upon the second signal ve2.

[0028] In an alternative embodiment, it is provided that the diagnostic block 17 acts directly on the second signal ve2, corresponding to FIGS. 2B and 3B. This embodiment is illustrated in FIG. 5 as a dash-dotted line. At the point in time t2, the diagnostic function detects that the engine torque MK is not plausible. As a reaction thereto, the signal ve2 is controlled according to the transition function from the value of point C to the value of point D, point in time t3, by means of the signal ve2D. The temporal course between the two points C and D can be constructed as a mathematical function or filtering function; signal course ve2(1) and ve2(2).

[0029]FIG. 6 is a program flow chart of the diagnostic function. In Step S1, the function is initialized and initial values are set. In Step S2, it is checked whether an error was detected; that is, whether the engine torque MK is plausible. If no error was detected, the normal mode (FM=0) is set in Step S3 and a waiting loop is implemented. If an error was detected in Step S2, an error mode (FM=1) is set in Step S4. The controller mode RM is queried in Step S5. The controller mode RM corresponds to 1 when the determination device, thus the rotational speed controller 14 or the function block 20, is dominant. In this case, this mode is retained, step S8. The controller mode RM corresponds to 2 when the torque controller 15 is dominant. In this case, a change of the dominance takes place in Step S6 from the torque controller 14 to the determination device. In Step S7, in addition, the limit value curve (DBR) of the maximally permissible first signal ve1 is adapted. In practice, this corresponds, for example, to the reduction of the maximally permissible injection quantity. In Step S9, the first signal ve1 is set as the power-determining signal ve. Subsequently, it is checked in Step S10 whether the error still exists. If this is so, the process is continued in Step S5. If it is determined in Step S10 that an error is no longer present, the error mode FM is set back to zero in Step 11, with the expiration of a time step. In Step S12, a return takes place to the normal mode. Then, the program flow chart branches to Point A and continues with Step S2.

[0030] List of Reference Numbers

[0031]1 Internal-combustion engine

[0032]2 turbocharger

[0033]3 fuel tank

[0034]4 first pump

[0035]5 throttle valve

[0036]6 second pump

[0037]7 high-pressure accumulator (rail)

[0038]8 injector

[0039]9 pressure sensor

[0040]10 rail pressure sensor

[0041]11 electronic engine control unit

[0042]12 engine load

[0043]13 clutch

[0044]14 rotational speed controller

[0045]15 torque controller

[0046]16 selection device

[0047]17 diagnostic block

[0048]18 function block detecting/filtering

[0049]19 rotational speed sensors

[0050]20 function block

[0051]21 characteristic diagrams

[0052]22 minimal value

[0053]23 function block computation P-fraction

[0054]24 function block computation I-fraction

[0055]25 function block computation D-fraction

[0056]26 summation

[0057]27 minimal value 

1. Diagnostic function for an internal-combustion engine (1) whose power is set by way of a power-determining signal (ve) in that, from a desired value definition (FP, nMOT(SW)), by means of a determination device (14, 20), a first signal (ve1) is determined, from the engine torque (MK), by means of a torque controller (15), a second signal (ve2) is determined (ve2=f(MK), and, by means of a selection device (16), the determination device or the torque controller (15) is set to be dominant for the power-determining signal (ve) (ve=ve1; ve=ve2), an error mode (FM) being set when the values of the engine torque (MK) are not plausible (FM=1), with the setting of the error mode (FM=1) when the determination device (14, 20) is dominant, the dominance being retained, and, when the torque controller (15) is dominant, a change of the dominance being implemented.
 2. Diagnostic function according to claim 1, characterized in that, when the error mode (FM=1) is set, the change of dominance is implemented from the torque controller (15) to the determination device (14, 20) according to a transition function by means of a diagnostic block (17).
 3. Diagnostic function according to claim 2, characterized in that, according to the transmission function, the engine torque (MK) is controlled from the last plausible value to zero (MK=0).
 4. Diagnostic function according to claim 2, characterized in that, according to the transition function, the second signal (ve2) is controlled from the last plausible value to a high value (ve2=MAX).
 5. Diagnostic function according to claim 3 or claim 4, characterized in that the transition function is implemented as a mathematical or filtering function.
 6. Diagnostic function according to one of the preceding claims, characterized in that, when the error mode (FM=1) is set, a limit value curve (DBR) of the maximally permissible first signal (ve1) is adapted.
 7. Diagnostic function according to claim 6, characterized in that the limit value curve (DBR) is adapted toward smaller values of the first signal (ve1).
 8. Diagnostic function according to one of claims 1 to 7, characterized in that the error mode (FM) is set back (FM=0) when plausible values of the engine torque moment (MK) are detected again, and a time step (t) has expired (t=0). 